Zirconium ternary alloys



ZIRCONIUM ALLOYS Lyle L. Marsh, Jr., and Walston Chubb, Columbus, Ohio,

assignors to the United States of. America .as repre.

"sented by the" United States Atomic Energy Gommission No Drawing. Application July 12, 1954,

Serial No. 443,984

1; Claim. (Cl. 75-171 The present invention is concerned with zirconium base alloys and particularly with zirconium-niobium base ternary alloys.

, The development of nuclear reactors for power applications and of ,cyclotrons, linear accelerators and similar apparatus subject to radioactivity and high temperatures" wherein zirconium is the predominant component and alloys should have a much lower neutron capture cross section than the stainless steels. Furthermore, the alloys' must have sufficient workability to enable them to be fabricated into simple shapes.

While such elements as aluminum, lead, molybdenum,

niobium, tantalum, tin, titanium and vanadium can all be used to strengthen zirconium effectively in binary alloys, it has been found in general that reasonable strength can be achieved only by sacrificing ductility or hy increasing the thermal-neutron capture cross section of the alloy to an undesirable extent. This results from the fact that no element has been found as; yet which has the combination of a high solubility in alpha zirconium, a low thermal-neutron capture cross section, and" a satisfactorilyhighboilingpoint; [J i :ltsisfan object ;of the pr'e'sent-inventibn'toprovide novel alloys havingitensilej characteristics 1 at 'high 'temperatures approximately equivalent to that; ofis'tainlss steel and satisfactory ductilitycharacteristics at high temperatures, but' haviiigcapture -cros's' sections 'for' thermalneutronsdessi-than one-third'the capture cross sectionbf stainless steel.

In accordance with the present invention it has been 2,784,084 l Patented Mar. 5, 1957 the weight percent of niobium presentexceeds the weight percent of the third metallic component.

Zirconium is a transition element characterized by-an1 incomplete inner shell of d electrons and an allotropic transformation at 865 C., transforming from a hexag, onalcrystal structure into a high-temperature body-. centered cubic structure. The three minor components of- 'the ternary alloys, namely, aluminum, vanadium, and mo lybdenum all have interatomic distances less than that of zirconium and lying within the range of the Hume- Rothery Rule. The percent difference of the interatomic distance of the third component from that of zirconium is:-- aluminum, -10%; molybdenum, 13%; and vanadium, 16%. It may be noted that the percent difference of the interatomic distance of niobium compared to that of zirconium is -9%.

The alloys may be produced by conventional methods. For the experiments described below the alloys were pre-. pared by drilling holes in pieces of metallic zirconium; putting suitable quantities of the two minor components into these holes and then filling the holes with zirconium chips. These zirconium pieces were then heated in a graphite crucible'by high-frequency induction at an absolute pressure of less than 10 microns of mercury. A

charge of about 200 grams is melted in each case; the

crucible is first charged with about half this quantity and after this first portion has melted the remainder of the charge is added. The melted alloys are then allowed to cool slowly. The ingots obtained thereby weigh between 1,60 and grams,-part of the material having been taken up by the graphite of the crucible.

The alloys were also produced in arc-melting iurnacesjv and satisfactory results were obtained by this method. 5 During the melting in the graphite crucibles a'small amount of carbon, up to about 0.5% by weight, was picked up by the alloys. A comparison of the high-temperature tensile strength of the alloys showed a very definite trend in favor of the arc-melted alloys over the. induction-melted alloys. This may be caused in part by the strengthening effect of the small amount carbon.

present.

off from the surface on each side in order to remove any gaseous contaminants. The scalped slabs were then cold-rolled in reductions of approximately 0.002 inch per pass until a total reduction of from 20 to 30% had been obtained. The cold-rolled alloys were then annealed for one hour at 700 C. in a straightening press. The sheaths resulting thereby were again scalped 0.018 inch on one side and cut into testing specimens. The hardness was determined at three stages of the alloys, namely, ascast, cold-rolled, and annealed, and the results are tabulated in the following table.

For the tensile strength tests, specimens inches long, /5 inch wide, and 0.04 to 0.08 inch thick were prepared. The reduced section was 1.5 inches long and 1 inch wide. The specimens were tested at 500 C(in an argon atmosphere. The speed of travel of the head of the testing machine was 0.02 inch per minute and an extensometer with a one-inch gauge length and an accuracy of plus or minus 0.0001 inch per inch was used to measure extensions. The extensometer was of the clip-on type with slide bars extending out of the heated area around the specimen.

The results of these tensile tests are shown in Table II. The tests were run in duplicate on each alloy and the results shown in Table 11 represent the average values obtained from these tests. The values listed under uniform elongation" represent the total elastic and plastic deformation at maximum load. The tensile strength of the zirconium-niobium binary alloy is shown for purposes of comparison.

Properties of zirconium alloys compared with properties of stainless steel at 500 C.

Thermal- Neutron Capture Cross Section,

barns/atom Yield Strength Ratio 1 Cross Section Alloy Analysis, w/o

( Ratio 1 Balance Zr) Type 347 Stainless Steel. Iniduction-Melted Zircon- 1 Based on 0.18 barn/atom tor zirconium.

5 Based on 2.86 barns/atom for stainless steel. 1

3 Based on a yield strength oi 31,000 p. s. i. for stainless steel at 500 C. The 1.5 niobium plus 1.0 aluminum ternary alloy is particularly outstanding, both in regard to yield strength ratio which is better than type 347 stainless steel at 500 C., cross section ratio which is' less than ,5 as great as stainless steel, and ductility (as shown in Table II) which is several times better.

It will be understood that this invention is not to be limited to the details given herein but that it may be moditied within the scope of the appended claim.

What-is claimedis:

A ductile zirconium base ,alloy consisting-essentially of TABLE I1 Tensile properties of zirconium alloys at 500 C.

Tensile Properties-M 500 0.

Alloy Analysis, w/o Yield Ultimate Elongation to Total Elongn= Strength Strength, Max. Load, tion in 1 in., Reduction oi (0.2% Offset), 1,000 p. s. i. Percent Percent Area, Percent 1,000 p. s. i.

1.0 Not-0.5 Al 26. 5 89. 3 30 30 31 1.5 NIH-1.0 A1 34.3 44.7 6 27 31 1.8 NIH-0.6 M 17. 8 28. 8 8 30 30 1.4Nb+1.1 M0 20. 9 32.5 4- 43 2.0 Nb+1.6 Mo 29. 3 38. 4 2 42- 48 1.0 Nb+0.3 V.- 16. 5 26.6 6" 30 39 1.3 Nb-l-l .1 V 20. 5 32. 7 7 21 26 2.2 Nb 35 43 9 15 6.0 Nb 36. 3 52. 4 3 8 5 may best be illustrated by comparing the yield strength 1.5 weight percent niobium, 1.0 weight percent aluminum, and zirconium and characterized-by having a thermal neutron capture cross section of 0.19 barn per atom and a 0.2% offset yield-strengthat 500 C. of 3430011. s. i.

References Cited inthe-filc of patent Schwope et-al.: Journal of Metals, November 1952. pages 1138-4140. 

